U.S. patent number 4,089,918 [Application Number 05/643,631] was granted by the patent office on 1978-05-16 for process for the continuous casting of liquid polymerizable compositions.
This patent grant is currently assigned to Sumitomo Chemical Company, Limited. Invention is credited to Yasuyuki Kato, Masahiko Moritani, Seiichi Suzuki.
United States Patent |
4,089,918 |
Kato , et al. |
May 16, 1978 |
Process for the continuous casting of liquid polymerizable
compositions
Abstract
A process and apparatus for the continuous casting of a liquid
polymerizable composition comprising feeding the liquid
polymerizable composition together with a pair of continuous
gaskets into a spacing between a pair of moving endless belts
arranged such that the lower run of the upper belt is disposed
above the upper run of the lower belt and said runs are driven
concurrently in the same direction at substantially the same speed,
said gaskets being fed such that they circumscribe both side end
portions of the spacing to form a cavity, while moving together
with the moving belts and keeping in contact with the opposing
surfaces of the belts. Passing the composition through a portion of
the path of the belts to partially polymerize said composition to
such a viscosity that a common logarithm of its viscosity in terms
of poise at the temperature of polymerization is within the range
of 2 to 5, then passing a portion of the path thereof arranged so
as to be curved at least once to bring its degree of polymerization
within the range of 40 to 60 weight per cent, and thereafter
passing the composition through a straight portion of the path for
complete polymerization, said path for polymerization being
arranged such the lower and upper runs of the respective belts are
brought closer together to follow shrinkage of the composition upon
polymerization. Finally the resultant polymerized plate product
with a good preciseness in thickness in the widthwise direction and
with favorable surface qualities is removed, from the discharge end
of the belts.
Inventors: |
Kato; Yasuyuki (Niihama,
JA), Moritani; Masahiko (Niihama, JA),
Suzuki; Seiichi (Niihama, JA) |
Assignee: |
Sumitomo Chemical Company,
Limited (Osaka, JA)
|
Family
ID: |
11564637 |
Appl.
No.: |
05/643,631 |
Filed: |
December 23, 1975 |
Foreign Application Priority Data
|
|
|
|
|
Dec 25, 1974 [JA] |
|
|
49-3700 |
|
Current U.S.
Class: |
264/40.7;
264/166; 264/216; 264/236 |
Current CPC
Class: |
B29C
39/006 (20130101); B29C 39/16 (20130101) |
Current International
Class: |
B29C
39/00 (20060101); B29C 39/16 (20060101); B29D
007/14 () |
Field of
Search: |
;266/216,166,40.7
;264/236 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Woo; Jay H.
Attorney, Agent or Firm: Birch, Stewart, Kolasch &
Birch
Claims
What we claim is:
1. A process for continuously casting a liquid polymerizable
composition which comprises feeding the liquid polymerizable
composition, together with a pair of continuous gaskets, into a
spacing defined between the lower run of the upper belt and the
upper run of the lower belt both of which are arranged such that
the pair of the endless belts are driven concurrently in the same
direction at substantially the same speed, said gaskets being
arranged so as to circumscribe the spacing serving as a pair of
seals to confine a cavity whilst moving concurrently with the belts
in contact with the opposing surfaces of the belts, passing the
composition through a portion of the path of the belts where said
composition is partially polymerized to such a viscosity that a
common logarithm of its viscosity in terms of poise at the
temperature of polymerization is within a range of 2 to 5, passing
the resultant composition through a portion of the path thereof
which is arranged so as to be curved at least once until the
composition reaches a degree of polymerization within a range of
about 40 to 60 weight percent based on the total weight of the
composition, and thereafter passing through a straight portion of
the path thereof for complete polymerization, while heat is applied
to substantially the entire path thereof, said path for
polymerization being arranged such that the lower and upper runs of
the respective belts are brought closer together to follow
shrinkage of the composition during the course of the
polymerization, and removing the polymerized plate from the end
portion of the belts at the discharge side thereof.
2. A process according to claim 1 wherein the composition is
partially polymerized to provide a composition having such a
viscosity that the common logarithm of its viscosity in terms of
poise is in the range of 2.7 to 4.
3. A process according to claim 1 wherein the liquid polymerizable
composition comprises at least one polymerizable, unsaturated
monomer which is a methacrylate, styrene or a derivative thereof
having at least one halogen atom and/or alkyl group substituent or
a mixture thereof with a monomer containing at least one
unsaturation copolymerizable with the monomers and which is an
acrylate, acrylonitrile or a derivative thereof or a
poly-functionally unsaturated monomer having at least two
unsaturations and which is glycol dimethacrylate, diallyl
methacrylate, diallyl phthalate, diethylene glycol or bisally
carbonate.
4. A process according to claim 3 wherein the liquid polymerizable
composition comprises methyl methacrylate.
5. A process according to claim 1 wherein a polymerization
initiator is included in the polymerizable composition in the
amount of from 0.005 to 5 percent by weight based upon the weight
of the liquid polymerizable composition.
6. A process according to claim 5 wherein the polymerization
initiator is at least one azo compound which is
azobisisobutyronitrile, azobisdimethylvaleronitrile, or
azobiscyclohexanenitrile, or at least one peroxide which is benzoyl
peroxide, lauroyl peroxide, acetyl peroxide, caproyl peroxide,
2,4-dichlorobenzoyl peroxide, isopropyl peroxy dicarbonate,
isobutyl peroxide, acetyl cyclohexylsulfonyl peroxide or
bis(4-tert.-butylcyclohexyl)peroxydicarbonate or a mixture of an
initiator of the former type with an initiator of the latter
type.
7. A process according to claim 1 wherein the polymerization is
carried out at a temperature in the range of from 50.degree. to
150.degree. C.
8. The method of claim 1, wherein the moving belts are conveyed
through a curved path at least once at a radius of curvature
determined by the following equation:
where R is the radius of curvature (in meters); S is an initial
tension strength applied to the belt (in kilograms per square mm);
T is the thickness of the belt (in mm); and K is a constant from
about 2 to 100.
Description
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to a process and apparatus for the
continuous casting of a liquid polymerizable composition. In
particular the present invention relates to a process in which the
liquid polymerizable composition is continuously fed into a spacing
defined between a pair of moving endless belts and formed into
plates.
Cell casting is in general known as a process for the preparation
of plates of polymers from polymerizable monomers by the
application of heat or light. The cell casting has been employed,
for example, for the preparation from methyl methacrylate of plates
of methacrylic resins having desirable properties including
transparency, surface gloss and weatherability. The cell casting is
a method in which a liquid monomer such as, for example, methyl
methacrylate or a syrup containing in part its polymerized
compounds is cast in a cell into which two sheets of reinforced
glasses are assembled with their outer peripheries sealed with
flexible gaskets. The cell casting process involves polymerization
of said liquid monomers fed into such a cell that is immersed in a
hot water bath or in a hot air oven and the stripping of the
resulting plates from the cell by separating the assembled cell.
Accordingly, the applicability of conventional cell castings may be
largely restricted by the size of the glasses used. This method
involves a series of staged operations such as the cell assembly,
the feeding of liquid monomers and the separation of the assembly,
so that it requires a great deal of manual work. Consequently, this
method raises the cost of product, and there has been a growing
demand for continuous casting process.
Some continuous casting processes are known, for example, U.S. Pat.
Nos. 2,500,728, 3,371,383, and 3,376,371. Japanese Patent
Publication No. 41,602/1971, and Canadian Patent No. 895,406. Each
discloses a process for the preparation of a plate of a polymeric
material which comprises filling with a polymerizable material a
spacing defined between a pair of endless belts, the first belt
being disposed above the second belt, and completing polymerization
during the movement of the belts. These processes, however, result
in a non-uniformity of the thickness of the resulting plates.
Particularly, the main difficulty involved in conventional
continuous casting processes is the loss of control over the
thickness of the final plate product in a widthwise direction. For
example, Canadian Patent No. 895,406 discloses a process in which
one of the two belts is so curved that the pressure applied by the
other belt is made uniform, thus preventing the warping, waving or
rippling of the belts. However, the process disclosed therein is
not satisfactory in that control of the precise thickness of the
final product is not achieved and the surface quality of the final
product, particularly in the widthwise direction, is impaired.
It is therefore the primary object of the present invention to
provide a process for the continuous casting of a liquid
polymerizable composition which can overcome or reduce to a
considerable extent the disadvantages of prior art continuous
casting processes.
Another object of the present invention is to provide a process for
continuously casting a liquid polymerizable composition which
comprises feeding the liquid polymerizable composition into a
spacing defined between a pair of moving endless belt conveyors,
polymerizing it partially to a viscosity in a specified range,
passing the partially polymerized composition through a path which
is arranged so as to curve at least once, until a degree of
polymerization of the resulting partially polymerized composition
reaches a predetermined value, and then passing it through a path
which is arranged in a straight direction for completion of the
polymerization of the partially polymerized composition.
Another aspect of the present invention is an apparatus for
continuously casting a liquid polymerizable composition by the
process according to the present invention.
Other objects, features and advantages of the present invention
will become apparent in the following description of the
specification and from the accompanying drawings and from the
appended claims, in which:
FIGS. 1 and 2 are each a schematic diagram of the apparatus of the
present invention.
According to the present invention, there is provided a process for
continuously casting a liquid polymerizable composition which
comprises feeding continuously the liquid polymerizable composition
into a cavity confined by a spacing defined between a pair of
moving endless belts and between a pair of continuous peripheral
gaskets, said moving endless belts being arranged such that the
lower run of the upper belt is disposed above the upper run of the
lower belt and the respective runs are allowed to move concurrently
in the same direction at substantially the same speed, and said
gaskets being fed in the side edges of the spacing such that they
can circumscribe both edges of the spacing while allowing the
liquid composition to travel through a path in a polymerization
region in which the composition is partially polymerized to such an
extent that a common logarithm of the viscosity of the composition
in terms of poise at the temperature of polymerization is within a
range from 2 to 5. The resulting partially polymerized composition
is passed through a path which is arranged so as to curve at least
once at a suitable radius of curvature until the composition is
further polymerized partially to provide a composition having a
degree of polymerization within a range of about 40 to 60 weight
percent based on the total weight of the composition. The
polymerization of the partially polymerized composition is
completed by passing through a path which is arranged in a straight
direction, and removing the plate of the polymerized composition
from the belts opposite to the feed side of the moving belts. The
spacing defined between the moving belts is arranged such that the
lower run of the upper belt and the upper run of the lower belt are
brought closer together, whereby contact between the composition
and both belts is maintained during the polymerization in response
to the volume variation of said composition. Using this process,
plates of polymeric material are prepared from a liquid
polymerizable composition, which have a uniform thickness,
particularly in the widthwise direction, and a good surface quality
is obtained.
In another aspect the present invention provides apparatus for the
continuous casting of a liquid polymerizable composition which
comprises a pair of endless belts which are arranged and
constructed such that the lower run of the upper belt is positioned
above the upper run of the lower belt to provide a space sefined
between the belts at a desired predetermined distance, said runs
being arranged so that the path between the runs is provided with a
region where it is curved at least once at a given radius of
curvature and thereafter with a region where it is maintained
straight. A pair of continuous gaskets are arranged such that they
circumscribe the spacing defined between the belts at both edges to
from a cavity and which can move together with the movement of the
belts while remaining in contact therewith to form a pair of seals
to confine the liquid polymerizable composition in the cavity,
means for adjusting the cavity between the runs to a desired
predetermined thickness, means for adjusting the cavity in response
to the variation of the volume of the composition which takes place
with the advancement of the polymerization, and means for driving
the belts in the same direction at substantially the same
speed.
The material for the endless belts used for the apparatus according
to the present invention may be a metal such as steel or stainless
steel. A plastic film may be employed together with a metal belt by
superimposing the film thereon. In general, the thickness of the
metal belt is from about 0.1 to 3 mm. and preferably from 0.5 to 2
mm.
The liquid polymerizable composition to be used in the present
invention comprises one or more unsaturated monomers which are
liquid under normal pressure. The composition may be partially
polymerized, prior to the introduction into the moving belts, to
such an extent that it may be fed into a spacing between the two
conveyor belts without any undesirable effect. If the composition
is used as a syrup in which the polymerized compositions are
dissolved, it is preferred to use a syrup having a viscosity in the
range in which the fluidity thereof is not impaired by feeding it
between the moving belts. The viscosity of the syrup may be
generally up to about 30 poises.
The unsaturated monomers which may be used as the liquid
polymerizable composition in the present invention include, for
example, methacrylates, styrene and its derivatives having at least
one halogen atom and/or alkyl group substituents, particularly
lower alkyl groups having from 1 to 6 carbon atoms or a mixture
thereof with a monomer containing at least one unsaturation which
is different from and copolymerizable with the said unsaturated
monomers, such as acrylates, acrylonitrile or derivatives thereof
or a polyfunctionally unsaturated monomer having at least two
saturations. The monomers of the type different from and
copolymerizable with the methacrylate, styrene or derivatives
thereof may be employed preferably in an amount up to about 20
percent based on the total weight of the liquid polymerizable
composition. Examples of the poly-functionally unsaturated monomers
are glycol dimethyacrylate, diallyl methcarylate, diallyl
phthalate, diethylene glycol and bisallyl carbonate. The process of
the present invention is particularly suited for the polymerization
of methyl methacrylate. The liquid polymerizable composition of the
present invention may also contain conventional additives such as
colouring agents, ultraviolet ray absorbers, thermal stabilizers,
plasticizers, stripping agents and/or fillers.
The liquid polymerizable composition may be introduced into a
cavity defined between the moving belts in conventional manner. For
this purpose, the apparatus of the present invention may be
provided with a device for feeding the composition in an
appropriate amount for each time successively into the moving
belts. Moreover, the apparatus may be equipped with a device for
preventing a drop of the lower run of the upper belt toward the
upper run of the lower belt by the aid of the liquid pressure.
The polymerization of the liquid polymerizable composition
generally proceeds in accordance with radical polymerization
reactions known per se in the art. The temperature for the radical
polymerization reaction is generally in the range of from
50.degree. to 150.degree. C., although it is not limited to this
range. Examples of polymerization initiators capable of forming
radicals in the above-mentioned temperature range are azo compounds
such as azobisisobutyronitrile, azobisdimethylvaleronitrile, or
azobiscyclohexanitrile, and peroxides such as benzoyl peroxide,
lauroyl peroxide, acetyl peroxide, capryl peroxide,
2,4-dichlorobenzoyl peroxide, isopropylperoxydicarbonate, isobutyl
peroxide, acetyl cyclohexylsulfonly peroxide or
bis(4-tert.-butylcyclohexyl)-peroxydicarbonate. The polymerization
initiator may be used alone or in combination. The amount of the
polymerization initiator is generally in the range of 0.005 to 5
percent by weight based on the weight of the liquid polymerizable
composition.
In a region of the path starting from point A (so referred to
herein) through which the liquid polymerizable composition is
caused to partially polymerize, heat is applied to the composition
outside the belts. The heating may be effected in various ways such
as spraying hot water on the external surface of the moving belts;
passing the moving belts through a hot water bath; steaming the
moving belts; or exposing the moving belts to infrared radiation.
The temperature of this polymerization region may be kept at a
constant level throughout its whole region where polymerization
takes place, or may be changed continuously or stepwisely in an
appropriate manner. The polymerization temperature may be chosen
depending upon the type and amount of polymerization initiator.
The liquid polymerizable composition of the present invention which
was fed into a cavity between the belts and between the peripheral
gaskets is first passed through a zone where partial polymerization
is caused to take place by the application of heat, to such an
extent that a common logarithm of the viscosity of the composition
in terms of poise at the temperature of polymerization is within
the range from 2 to 5, preferably from 2.7 to 4. If the viscosity
of the composition is such that the common logarithm thereof is
below the lower limit at the point where the first curve in the
path begins, the composition tends to leak from the cavity defined
between the moving belts during the course of polymerization,
thereby making it difficult to obtain a satisfactory final product
or providing a non-uniform thickness of the polymer plate. A
viscosity of the composition above the upper limit expressed as the
common logarithm thereof is not desirable, too, because the
non-uniformity in the thickness of the final product results and,
particularly, preciseness of the thickness of the plate lacks in a
widthwise direction.
The path of the moving belts from a point where the composition is
fed into the spacing defined between the belts to point B may be
straignt in a horizontal direction or in such a manner as inclined
at an appropriate angle to the horizontal or may be curved to
follow a natural curvature that may be defined by the moving belts
when arranged so as to be inclined at a suitable angle to the
horizontal.
The thermal polymerization zone up to point B is provided with a
mechanism for adjusting and maintaining the space between the belts
in a desired thickness and at the same time preventing the leakage
of the composition out of the space between the belts by arranging
a pair of the peripheral gaskets so as to bring the opposing
surfaces of the lower and upper runs of the respective belts at
their opposing edges in contact therewith. This mechanism may be
designed so as to be capable of compensating for any variation in
volume of the composition during polymerization. Such mechanism may
also be empolyed in combination with a mechanism for bringing the
surfaces of the belts closer together to an extent sufficient to
compensate for any shrinkage of the composition during
polymerization. In this thermal polymerization zone is provided a
rotatable support member such as a roller or a non-rotatable
support member having a smooth roll surface for the purpose of
supporting the moving belts and bringing the surfaces of the belts
closer together to follow the volume change of the composition.
This partially polymerized composition is then led to a zone where
a pair of the belts are curved at least once in such a manner as
having an appropriate radius of curvature as will be defined
hereinbelow. Point B is also the point where the belts begin to
curve. The number of the curves of the belts is not limited hereto,
and the belts may be curved a plurality of times. The adjacent
curves are connected with each other through an inflection point,
that is, a point where two curves meet (hereinafter referred to in
general as point C). Thus the belts having two curves possess one
inflection point. It is preferred to provide the path of the belts
with two curves through one inflection point. The belts may also
have a substantially straight portion between adjacent curves, the
straight portion between the adjoining curves may be arranged so
that it has a common tangent to the two curves at a common
inflection point. However, the straight portion should not be too
long because it may impair the effect to be achieved by providing
the belts with the curves. The belts are also designed so that they
travel through a straight path after a point where a series of
curves ends (hereinafter referred to as point D).
The polymerization of the partially polymerized composition further
proceeds during the course of the curved path by applying heat
thereto in the same manner as described hereinabove. In this region
is preferably provided a rotatable support member such as a roller
for the purpose of supporting the moving belts, whereby the
surfaces of the moving belts are allowed to be brought closer
together in response to the volume change of the composition during
polymerization. Where a portion of the path curves concavely, the
belts may be arranged and constructed such that the lower run of
the upper belt is supported by means of a rotatable support member
such as rollers and the upper run of the lower belt is not
supported by such a support member and instead by its own tension
that can push the upper run thereof concavely in a direction
against the lower run of the upper belt, whereby the belts may
preferably allow to follow the volume variations of the composition
during the passage through the curved path, and vice versa. It is
preferred that such a mechanism for adjusting and maintaining the
space between the belts in a desired given thickness is also
provided in this zone.
Where a moving belt made from the said metal, for example stainless
steel, is employed, the radius of the curves which begin at point B
may be represented by the following equation:
R = K .times. S .times. T
where R is the radius of curvature (in meters); S is an intial
tension strength applied to the belt (in kilograms per square
millimeter); T is a thickness of the belt (in millimeters); and K
is a constant. The constant K is a value that varies with the
initial tension strength S and the thickness T of the belt and may
range preferably from 2 to 100. Where the belts are curved twice,
the radius of the first curve starting from point B can be
calculated by the constant K being within the range of 2 to 100,
and that of the second curve may not be limited to the value in
which the upper limit of the constant K is not particularly limited
to said value. Where the constant K is below the lower limit, the
lower and upper runs of the respective upper and lower belts, which
are arranged to move in the same direction at substantially the
same speed, tend to slide slightly out of position, thus causing a
relative movement between the runs so that the surfaces of the
plates of polymeric material are impaired. This is also a
disadvantage because of the stress being put on the moving belts.
The lower limit of the curvature radius may be chosen by a force
given by the pressure of the belts, which can prevent the
countercurrent flow of the liquid composition disposed between the
belts at point B. That is, the pressure given by the belts should
be determined in such a manner that it becomes smaller than the
liquid pressure of the composition at point B. Where the curvature
radius is fairly greater than a value when calculated as K being
the said upper limit, this may reduce the effect expected to be
achieved by providing the belts with curves in a specified manner,
and the thickness of the plate does not become uniform particularly
in a widthwise direction. Thus, a plate of polymer having a uniform
thickness, particularly in a widthwise direction precisely
satisfying a desired value can be obtained where the belts are to
be curved at least once from point B and the constant K is within
the above range.
The liquid polymerizable composition is allowed to polymerize
partially to a degree of polymerization within the range of about
40 to 60 percent by weight based on the weight of the composition,
during the passage through the curved path of the belts. The
partially polymerized composition is then led to a zone in which
the belts are disposed in a straight direction. The point at which
this zone starts will be referred to as point D in the following
specification. Since the composition at point D in a jelly-like or
agar-like form, its viscosity is not to be measured. Since the
composition at this point undergoes a maximum decrease in its
volume due to rapid variations in its degree of polymerization, it
is characterized physically, at point D, by its degree of
polymerization. Where the degree of polymerization at point D is
less than the said lower limit, it is not desired because the
resulting plate of the composition tends to cause a non-uniformity
in thickness, particularly in a widthwise direction. Where the
degree of polymerization at point D is greater than the upper
limit, the resulting plate will exhibit an undesirable surface
quality and, particularly, tends to be caused a wavy pattern in a
widthwise direction on its surface. The plate of polymeric material
with a uniform thickness, particularly in a widthwise direction,
and a good surface quality, where the degree of polymerization at
point D is defined within the given range.
The partially polymerized composition having a degree of
polymerization within said range is then led to the path which is
arranged and constructed so as to be in a straight line from point
D to a point where the straight portion ends (hereinafter referred
to as point F). Point F is also the point of the end portion of a
mechanism for adjusting the space between the belts in response to
the volume change of the composition and the polymer plate formed
therefrom.
The straight portion is provided with a zone where the
polymerization is carried out by the application of heat and
thereafter with a zone where the composition is treated by the
application of heat. The end point at which the heat polymerization
zone terminates will be referred to hereinafter as point E. The
composition is further polymerized during the passage through the
region between points D and F, increasing its degree of
polymerization to a point of complete polymerization.
The heat polymerization zone provided after point D is arranged
such that the composition is caused to amount to a degree of
polymerization ranging from about 80 to 95 weight percent. This
zone comprises generally spraying or showering a hot water against
the exterior surfaces of the moving belts; steaming the exterior
surfaces of the moving belts; or running the moving belts in a hot
water bath.
The zone where the composition is treated by heat is arranged so as
to allow the composition to bring about complete polymerization.
This zone generally comprises applying infrared radiation or the
flow of hot air current to the exterior surfaces of the moving
belts. This heat treatment zone may be preferably arranged so as to
be in a position above the position of the heat polymerization zone
because the water used in the heat polymerization zone accompanies
the moving belts to the heat treatment zone and this makes it
difficult to maintain the heat treatment zone at a desired
temperature range. Thus, it is preferred to arrange the path
between points D and F so as to drive the belts in a straight
direction inclined at an appropriate angle to the horizontal,
positioning the heat polymerization zone below the heat treatment
zone. Where the composition does not reach the said lower limit in
its degree of polymerization at point E, it is also possible to
complete the polymerization in the heat treatment zone, although
this is not desired because the resulting plate of the composition
may be caused to contain bubbles therein.
The straight portion is further provided with a mechanism for
bringing the surfaces of the moving belts close together while
keeping them in contact with the surfaces of the polymer plate to
compensate for any shrinkage during polymerization. For this
purpose, a rotatable supporting member such as rollers or a
non-rotatable supporting member having a smooth surface may be
employed. These supporting members also serve as supporting the
moving belts so as to maintain the space between the belts at a
desired thickness. These supporting members may be arranged such
that they are designed so as to support the upper run of the lower
belt alone, while the lower run of the upper belt is designed so as
to allow the concurrent movement by its own weight together with
the polymer plate that is driven in association with the movement
of the lower belt.
The straight portion of the path of the moving belts from point E
to point F may be provided with a zone for cooling the polymer
plate at any suitable position after the heat treatment zone. The
cooling zone may be also positioned after point F. The cooling may
be accomplished in any conventional manner, for example, by blowing
cold air to the moving belts or by leaving it to stand in air after
discharged from the space between the moving belts.
Referring now to the drawings,
FIG. 1 illustrates a schematical side view of the continuous
casting apparatus of the present invention wherein the path defined
by the moving belts is curved once and supporting members are
provided at both sides of the belts; and
FIG. 2 illustrates a schematical side view of the apparatus of the
present invention wherein the belts are curved twice and supporting
members are provided in part.
FIGS. 1 and 2 are examples of the continuous casting apparatus of
the present invention in which the upper run of the lower belt is
longer than the lower run of the upper belt. These figures indicate
each a relative location of points A through F. As shown herein,
there are each the moving belts in which point A is positioned
above point B and the path between them is disposed in a straight
direction. It is further inidcated therein that the path from point
D is inclined upwardly to the horizontal so as to position point D
below points E and F.
As further shown in FIGS. 1 and 2, endless belt 1 is provided with
tension by means of a set of pulleys 3 and 4 and endless belt 2 is
by means of another set of pulleys 5 and 6. The pulleys 4 and 6 are
designed so as to drive at the same peripheral speed or either of
them is designed to drive and the other is arranged so as to be
caused to drive by the aid of the plate of polymeric material
and/or the gaskets between the moving belts. The liquid
polymerizable composition is fed continuously into the moving belts
at its inlet together with a pair of the continuous gaskets and the
resulting plate is discharged from the outlet between the moving
belts.
Referring specifically to FIG. 1, the lower and upper runs of the
respective belts in the path between points A and B are held and
maintained by means of a non-rotatable support 7 having a frame
structure, so as to provide a spacing defined between them at a
desired thickness. The path between points B and F is provided with
two sets of rollers, indicated generally by number 8, so that the
moving belts are held under tension and in a manner capable of
following the change in volume of the composition during the course
of polymerization.
Referring now to FIG. 2, the zone between points A and B is
provided with two sets of rollers 8 in order to hold the moving
belts under tension having a spacing defined between them at a
desired thickness. In the path between points B and F, a set of
rollers are arranged and constructed at the one side only so as to
cause the upper belt to curve in a manner satisfying the
requirement for the radius of curvature as specified above.
Specifically, the path between points B and C is provided with a
set of rollers 8 in such a manner that the rollers allow the lower
run of the upper belt to follow a concavely arcuate curvature
meeting the requirement for the radius of curvature as defined
hereinabove and the upper run of the lower belt is held under
tension by means of the pulleys 5 and 6, which is designed so as to
apply pressure to the upper belt in an upward direction and to
drive concurrently with the upper belt by the aid of the pressure
given by the belts held under tension by the pulleys 5 and 6. This
makes the moving belts capable of following in response to the
volume change of the composition during the course of
polymerization. In the path from point C to point D, a set of
rollers are provided only at the side of the upper run of the lower
belt in a manner converse to the previous path but functioning in
substantially the same manner as in the path from point B to point
C. Thus, the rollers 8 are arranged in such a manner that, where a
portion of the path is in a convexly arcuate curved manner, a set
of the rollers are positioned only on one side of the lower belt to
thereby forcibly guide a corresponding portion thereof to extend in
a convexly curved manner, while a corresponding portion of the
upper belt is adapted to follow the curve of that portion of the
upper run of the lower belt defined by said set of the rollers, by
the effects of tension exerted to the upper belt and of the weight
thereof.
FIGS. 1 and 2 show the embodiments of the apparatus according to
the present invention in which the pulleys 3 and 4 are positioned
on the same height. The respective position of the pulleys,
however, should be construed as being not limited thereto, and it
may be possible to position either of the pulleys above or below
the other. In order to lower the height of a housing of the
apparatus, it is desired to arrange both of the pulleys at the same
height.
Although FIGS. 1 and 2 illustrate a pair of the moving belts in
which the upper belt is shorter than the lower as described
hereinabove, it is not limited thereto and it may be possible to
arrange the belts in such a manner that the lower and upper runs of
the respective belts have the same length.
It is desired that a distance between a point of the pulley at the
feed inlet side and point A is as short as possible. This is true
of the length of the path between point F and a point of the pulley
at the discharge side and it may be possible to design point F to
come just below the center of the upper pulley at the discharge
side. By making these distances as short as possible, it can be
possible to make the path longer and effectively available for the
heat polymerization zone and the heat treatment zone. And the
cooling zone may also be provided with efficiency. This is
advantageous in terms of separating the plate of the composition
from the moving belts with ease.
The straight portion from point F to the discharge outlet may be
disposed in a horizontal manner of inclined at an appropriate angle
to the horizontal. This portion may be arranged so as to have a
spacing between the moving belts having a thickness thicker than
the thickness of the plate of the composition.
The gasket to be used for the present invention is generally of
filamentous plastic material. Examples of such materials are soft
polyvinyl chloride, polyethylene, polypropylene, ethylene-vinyl
acetate copolymer, natural rubber, rubbers of different type and
other flexible plastic materials. Soft polyvinyl chloride is in
general preferred and may preferably contain from about 80 to 170
parts by weight of a plasticizer such as dioctyl phthalate based on
100 parts by weight of the polyvinyl chloride. The cross section of
the gasket may be in any any shape such as square, rectangle or
circle, and the gasket in the form of a hollow pipe is generally
preferred.
The following examples illustrate the present invention without,
however, limiting the same thereto. In the following examples,
percent is by weight.
EXAMPLE 1
An apparatus having a construction as shown in FIG. 2 was employed,
in which a pair of stainless steel belts having a flat, polished
surface are each 500 mm. wide and 0.6 mm. thick; a mechanism for
adjusting a spacing defined between the belts to follow the volume
change of a liquid polymerizable composition is provided through a
heat polymerization zone and a heat treatment zone up to a cooling
zone; the belts are curved twice from point B; and a region from
point D to point F is maintained in a straight direction. In the
path through which the lower and upper runs of the respective upper
and lower belts travel, the horizontal distance is 3,500 mm. long
between points A and B; 1,489 mm. long between points B and C; 751
mm. long between points C and D; and 4,260 mm. long between points
D and F.
The straight portion from point A to point B is supported at both
sides of the belts by rollers and inclined at an angle of three
degrees to the horizontal. The portion between points B and C is
curved at a radius or 14,000 mm. and arranged such that the lower
run of the upper belt alone is supported by a set of rollers. The
curved portion from point C to point D has a radius of 39,213 mm.
and it is arranged so as to support only the upper run of the lower
belt by means of a group of rollers. The straight portion between
points D and F is inclined at an angle of two degrees to the
horizontal and designed such that the upper run of the lower belt
is supported by a group of rollers.
The portion between points A and E is a zone where the
polymerization is caused to occur by the application of hot water
having a temperature of 85.degree. C. The first portion having a
horizontal distance of 2,170 mm. from point E is a zone where hot
air having a temperature of 120.degree. C. was blown to the moving
belts. The second portion having a horizontal distance of 1,090 mm.
up to point F is a zone where a cool air is applied to the moving
belts.
A syrup having a viscosity of 4 poises at 25.degree. C. and
containing a solution of 14 percent of polymethyl methacrylate and
0.08 percent of azobisisobutyronitrile in methyl methacrylate was
continuously fed together with a pair of hollow, cylindrical
gaskets made of soft polyvinyl chloride containing 55 percent of
dioctyl phthalate from one side into a spacing between the moving
belts. The upper and lower belts are held under an initial tension
of 3 kilograms per square mm. and driven at a speed of 217 mm. per
minute. The distance between the belts at the portion from point A
to point B is arranged so as to thereby provide a plate product
having a thickness of 3 mm.
The viscosity of the partially polymerized composition at point B
was 1,250 poises and the degree of polymerization at point D was 58
percent.
The plate product was found to have a reduced viscosity of 3.3 dl
per gram at 25.degree. C. in a 0.1% chloroform solution and contain
0.9 percent of the methyl methacrylate residue. The thicknesses of
the plate product in a widthwise direction ranged from 2.95 mm. as
the minumum to 3.06 mm. as the maximum. This indicates that the
resulting product has a very favorable preciseness in thickness in
a widthwise direction, and the product possesses a very smooth,
excellent surface quality.
COMPARATIVE EXAMPLE 1
With the same apparatus employed in Example 1, a syrup having a
viscosity of 4 poises at 25.degree. C. and containing a solution of
14 percent of polymethyl methacrylate and 0.22 percent of
azobisisobutyronitrile in methyl methacrylate was caused to
polymerize under the same conditions as in Example 1. In this
example, the viscosity of the syrup at point B was found to be
400,000 poises and the degree of polymerization at point D was 94
percent.
The resulting polymer plate was found to have a reduced viscosity
of 2.1 dl per gram at 25.degree. C. in a 0.1% chloroform solution
and contain 0.6 percent of the methyl methacrylate as the residual
component.
The thicknesses of the plate product in the widthwise direction
varied to a considerably irregular extent, ranging from 2.58 mm. to
3.40 mm. and the product possessed wavy patterns in a widthwise
direction. This seems to be due to its high viscosity at point B
and its high degree of polymerization at point D.
COMPARATIVE EXAMPLE 2
The apparatus employed in Example 1 was used here except that the
path defined by the lower and upper runs of the respective belts
are arranged as follows: the horizontal distance from point B to
point C was 1,892 mm. long and curved at a radius of 17,000 mm.;
the horizontal distance between points C and E was 1,348 mm. and
curved up to point E at a radius of 56,015 mm, and the upper run of
the lower belt alone was supported by a group of rollers; and the
straight portion was 3,260 mm. long as the horizontal distance and
arranged so as to support the upper run of the lower belt alone by
means of a group of rollers, having an inclination at an angle of
2.degree. to the horizontal.
With the syrup used in Example 1, the reaction conditions employed
in Example 1 were repeated to thereby give a plate product having a
thickness of 3 mm. In this example, it was found that the degree of
polymerization at point E was 94 percent.
The resulting plate product was found to have a reduced viscosity
of 3.4 dl per gram at 25.degree. C. in a 0.1% chloroform solution
and contain 0.8 percent of the methyl methacrylate residue. It was
further found that it had thickness variations in the widthwise
direction ranging from 2.93 mm. to 3.08 mm. Although this plate had
a good preciseness in thickness, wavy patterns were formed on the
surface of the plate in a widthwise direction. This seems to be due
to a high degree of polymerization at a point where the straight
portion of the path began.
COMPARATIVE EXAMPLE 3
With the apparatus of Example 1, the portion between points A and F
was arranged straight and point A was positioned above point F in
such a manner as having an inclination at an angle of 3.degree. to
the horizontal. The belts are supported at their both sides each by
a set of rollers and divided into the respective zones in the same
manner as in Example 1.
The syrup in Example 1 was caused to polymerize in the same manner
as in Example 1 to give a plate having a thickness of 3 mm. This
plate was found to have a reduced viscosity of 3.1 dl per gram at
25.degree. C. in a 0.1% chloroform solution and contain 0.8 percent
of the methyl methacrylate residue. Although the surface quality of
the resulting product was good, e.g. having a smooth, excellent
surface, its thicknesses in the widthwise direction varied
irregularly, ranging from 2.55 mm. to 3.48 mm. This seems to arise
due to no curvature being provided in the path through which the
polymerization was effected.
EXAMPLE 2
The apparatus of Example 1 was arranged in which the straight
portion between points A and B had a horizontal distance of 2,900
mm.; the curved portion between points B and C had a horizontal
distance of 1,431 mm. and it was curved at a radius of 13,000 mm.;
the portion from point C to point D had a horizontal distance of
809 mm. and it was curved at a radius of 25,639 mm.; and the
straight portion from point D to point F had a horizontal distance
of 4,860 mm. and it was included at an angle of 1.5.degree. to the
horizontal.
A syrup having a viscosity of 4 poises at 25.degree. C. and
containing a solution of 14 percent of polymethyl methacrylate and
0.5 percent of lauroyl peroxide in methyl methacrylate was fed into
a spacing between the belts under the same conditions as in Example
1 except for the application of hot water having a temperature of
80.degree. C. instead of 85.degree. C. The viscosity of the
composition at point B was found to be 352 poises and the degree of
polymerization at point D was 48 percent.
The resulting plate having a thickness of 3 mm. was found to have a
reduced viscosity of 2.7 dl per gram at 25.degree. C. in a 0.1%
chloroform solution and contain 0.6 percent of the methyl
methacrylate residue. The thickness of the product in the widthwise
direction was found to be excellent, ranging from 2.92 mm. to 3.05
mm. It was also noted that its surface was smooth and excellent,
thereby giving a very favorable overall quality.
EXAMPLE 3
The apparatus employed in Example 1 was used in which the belts
were curved once from point B and the portion from point D to point
F was arranged straight. In this apparatus, the horizontal distance
between points B and D was 1,640 mm. and it was curved at a radius
of 17,736 mm. while the upper and lower belts in this curved
portion are supported each by a set of rollers; the straight
portion between points D and F had a horizontal distance of 4,860
mm. and it was inclined at an angle of 2.3.degree. to the
horizontal and supported at its both sides of the moving belts by a
set of rollers. The other apparatus arrangement was the same as
with that of Example 1. In this apparatus, the polymerization was
effected by applying water having 90.degree. C.
A syrup having a viscosity of 2 poises at 25.degree. C. and
prepared by polymerizing methyl methacrylate with 0.001 percent of
azobisisobutyronitrile at 80.degree. C. and dissolving additionally
0.08 percent of azobisisobutyronitrile in the resulting syrup was
allowed to polymerize under the same conditions as in Example 1 to
yield a plate having a thickness of 3 mm. The viscosity of the
syrup at point B was found to be 400 poises, and its degree of
polymerization at point D was 48 percent.
The plate product was found to have a reduced viscosity of 3.1 dl
per gram at 25.degree. C. in a 0.1% chloroform solution and contain
0.9 percent of the methyl methacrylate as the residual component.
The preciseness in thickness of the plate in the widthwise
direction were very good and they ranged from 2.87 mm. to 3.14 mm.
The surfaces of the plate were smooth and excellent in overall
surface quality.
EXAMPLE 4
An apparatus having a construction similar to that of FIG. 1 was
employed, in which the straight portion between points A and B had
a horizontal distance of 2,900 mm. and an inclination at an angle
of 3.degree. to the horizontal, while being supported by
non-rotatable supporting bodies having a frame structure; the
curved portion from point B to point D had a horizontal distance of
2,240 mm. and a radius of 25,423 mm. and it was supported at its
both sides of the belts by sets of rollers; the straight portion
between points C and D had a horizontal distance of 4,860 mm. and
an inclination at an angle of 2.1.degree. to the horizontal. The
region of the path where the lower and upper runs of the respective
belts follow was provided in the same manner as with the apparatus
used in Example 3, with zones where the polymerization was carried
out by the application of heat and the polymerized composition was
further treated by the heat application, and a zone where the
polymerized composition was cooled.
A syrup having a viscosity of 4 poises at 25.degree. C. and
containing a solution of 25 percent of polymethyl methacrylate and
0.02 percent of azobisdimethylvaleronitrile in methyl methacrylate
was introduced continuously, together with the gaskets used in
Example 1, into a spacing between the belts which were held under
an initial tension of 5 kilograms per square mm. for the upper belt
and under an initial tension of 4 kilograms per square mm. and
operated at a belt speed of 270 mm. per minute. The viscosity of
the syrup was 7,900 poises at point B and its degree of
polymerization was 47 percent at point D.
The resulting plate product that was prepared so as to have a
thickness of 3 mm. had its reduced viscosity of 3.5 dl per gram at
25.degree. C. in a 0.1% chloroform solution and contained 1.2
percent of the methyl methacrylate residue therein. Its thickness
in the widthwise direction ranged from 2.89 mm. to 3.11 mm.,
providing a very good preciseness in thickness and and at the same
time an excellent overall surface quality.
* * * * *